The alert is in effect through Sept. 1, 2017.

U.S. issues travel alert for Europe.
The Museum of the City of Brussels, Belgium.
| Credit: Fabio Canhim/Getty Images

The U.S. State Department issued a travel alert for all of Europe on Monday, alerting citizens to the potential risk of terrorist attacks.

The alert, which is intended to inform travelers rather than deter travel, states that U.S. citizens “should always be alert to the possibility that terrorist sympathizers or self-radicalized extremists may conduct attacks with little or no warning.” The alert expires on Sept. 1, 2017 (although alerts are frequently updated or extended).

Citing recent incidents in France, Russia, Sweden, and the United Kingdom, the State Department noted that busy urban hubs like tourist hotspots and markets, as well as transportation hubs, could be possible targets: “U.S. citizens should exercise additional vigilance in these and similar locations,” the alert states, “in particular during the upcoming summer travel season when large crowds may be common.”

This is not the first time the State Department has issued an alert for the continent: Last year, there was a similar alert that was not in reference to a specific threat but was instead issued ahead of large summer events with large crowds, CNN reported.